I think it's about raising revenue, would be a bonus to reduce crashes. Hopefully all this revenue goes to getting people out of motor vehicles and onto other modes.
There was a study several years back that concluded that speed and stoplight cameras actually increase crashes. Drivers often see them at the last moment and slam on the breaks then get rear ended or cause cars to swerve.
Don't drive faster than the speed limit? Shouldn't have to slam if your driving the limit.
Also drivers have seat belts, crumple zones and air bags. Pedestrians do not. The danger presented to a pedestrian is much greater than a driver whose rear ended at a red light.
I think more speed cameras and a lower limit would make a noticable difference. It's also fast to implement. With that said, a longer term goal should be to redesign roads to calm traffic more naturally.